SANTA CRUZ -- A 55-year-old homeless man who attacked another homeless man in downtown Santa Cruz was sentenced to 12 years in prison Wednesday.

The unprovoked attack in October 2012 left a 47-year-old man with a broken nose and broken bones near his eye, prosecutors said. It was Randy Ruben Reyes' third attack for which he was prosecuted in Santa Cruz County since 1993, said Assistant District Attorney Sara Dabkowski.

In March, a jury found Reyes guilty of battery causing serious bodily injury. Dabkowski called it a "brutal act of aggression on a helpless person" during the sentencing hearing in front of Judge Ariadne Symons.

The other man left and returned, walking with his head down. Reyes approached him, bent his knees and threw his full body weight into a punch that landed on the man's face, according to video surveillance footage and witnesses.

Reyes fled toward the Metro Bus Station, but a witness followed him and notified police.

The victim was transported to Dominican Hospital and later to Stanford Medical Center. The District Attorney's Office could not locate the man during Reyes' court proceedings because he is a transient.

Reyes and the other man usually stay in Santa Cruz, Dabkowski said.

"Reyes has a long history of violence dating back to the late 1970s," Dabkowski said in a statement.

During his sentencing hearing, Reyes said he had post-traumatic stress disorder from his childhood. He struggled with drug and alcohol abuse, he said, and sought help in the fall from the Department of Veterans Affairs because he had been in the Marine Corps.

In 1993, Reyes was convicted of felony assault in Santa Cruz County and again in 2002 for an attack in Boulder Creek, according to court records.

Reyes was on felony probation for threatening a police officer when he was arrested in the October battery.